Data Management, Transaction Models and Enabling Technology for Mobile Commerce

1. Data Management, Transaction Models and Enabling Technology for Mobile Commerce

2. In this discussion… • Introduction • Enabling Technology • Data Management • Transaction Models • Query Processing • Recovery

3. Introduction • E-commerce applications run on fixed, reliable networks. • M-commerce combines two independent technologies: wireless telecommunication and digital communication. • M-commerce applications work on unreliable wireless networks and involve end users applications, mobile devices, middleware. • M-commerce applications include financial applications, advertising, inventory management, product locating and shopping, mobile auction services etc. • In this session we discuss issues of data management, transaction management, query processing and recovery in mobile commerce applications

4. 2. Enabling Technology (WAP & GPRS) • Wireless Application Protocol (WAP): • WAP model provides architecture to develop and run applications on mobile devices. WAP content and applications are specified in a set of well-known formats. Content is transported using a set of communication protocols for wireless environment. • WAP defines a set of standard components. • Standard naming model for locating resources • Content typing for processing different types of data. • Standard content formats and • Standard communication protocol

5. The WAP Architectureprovides a scalable and extensible environment for application development for mobile devices in wireless environment. Each layer of the architecture is accessible by the layers above, as well as by other applications and services Fig 1: WAP Architecture

6. Wireless Application Environment (WAE): Provides interface to build and run applications of wireless environment Wireless Session Protocol (WSP): Offers both connectionless and connection oriented services and Responsible for long-lived session state, sessions suspend and resume with session migration, reliable and unreliable data push. Wireless Transaction Protocol (WTP): Provides unreliable and reliable one-way and two-way requests and transactions, asynchronous transactions and data unit concatenation.

7. Wireless Transport Layer Security (WTLS): Provides data integrity, privacy, authentication and protection to the upper layers. Wireless Datagram Protocol (WDP): Operates above the bearer services supported by the different networks and offers a consistent service to the upper layer protocols. Bearers: e.g. short message, circuit-switched data, and packet data.

8. GPRS (General Packet Radio Service) • GPRS is a bearer service for GSM (Global System for Mobile communications) • Greatly improves and simplifies wireless access to packet data networks. • Transfers data packets from GSM mobile stations to external packet data networks (PDN) using a packet radio principle. • Networks based on the Internet Protocol (IP) and X.25 networks are supported by GPRS. • GPRS uses a billing system based on amount of transmitted data rather than time of connection.

9. Fig 2: GPRS Architecture

10. Table 1: GPRS Interfaces

11. GPRS Services • Two types: • Point-To-Point (PTP) service • * PTP CNLS • * PTP CONS • 2) Point-To-Multipoint (PTM) service. • * PTM – M • * PTM – G • And additional services like messaging, database access, credit card validation etc.

12. 3. Data Management • Challenges: • Dissemination problems due to limited band width of the channel • susceptibility to interferences • limited battery power • security threat and • asymmetric communication i.e. downstream is larger than upstream.

13. Global data management : network level issues such as location, addressing, replication, broadcasting etc. Local data management: energy efficient data access management and query processing at the user level

14. Fig 3: Mobile database architecture

15. Location data management deals with the management of databases to store the information of user’s locations. Location databases are queried while routing to obtain the current location of mobile user. • Location databases are distributed in nature. • Location management involves searching, reading and updating the location databases.

16. Data access management Initiation Dissemination Publication Demand-driven Client (Pull) Server (Push)

17. Broadcast data organization is known as broadcast program or broadcast schedule. flat Cyclic Non-flat Broadcast program Acyclic

18. Fig 4: Broadcast programs

19. Broadcast Disks: (Acharya et al) uses cyclic, non-flat dissemination architecture. • provide a multi-level mechanism that permits non uniform broadcast of data items • devises mechanisms for storage management, client side caching and prefetching for efficient multi-level broadcast.

20. Data Indexing:Extra meta-data is added to data objects so that clients only need to selectively tune to broadcast channel to extract the desired data. • addition of indexing information increases the bandwidth requirement of the communication channel. • Indexing schemes should be evaluated in terms of a tradeoff between access time and listen time.

21. Performance Criteria ( TAARQ ) • Tuning time: Amount of time spent by client to listen the channel. • Adaptability: This is the ability of the model to cope up with the changing environment. • Average access time: It is the average time period between client’s requests and getting the requested data from the server. • Resource utilization: Resource utilization can be measured as data requests per unit battery power. • Query rate: Number of queries per unit time.

22. Data Replication and Consistency Management: Data replication - reduces access time - transparency of mobility Challenges - selection of data and service stations - updation of database - consistency management

23. Consistency Management: • “Session guarantees” address the problems of consistency management. • A session is a sequence of read and write operations in an application. • Session guarantees are developed and deployed in Bayou project. • The methods of session guarantees offered by session manager are: • Read your writes: read after write. • Monotonic Reads: read after read. • Write Follow Reads: write after read. • Monotonic Writes: write after write.

24. 4. Transaction Models • Reporting & Co-Transactions • Kangaroo • Clustering • Isolation-only • Two-tier • Team • Multi-database • Toggle • PRO-MOTION

25. Reporting and Co-Transactions(Chrysanthis) • Based on the open-nested transaction model. • Mobile transaction is a set of relatively independent transactions. • If a parent transaction aborts, all its uncommitted components may also abort. • classifies mobile transactions into the following four types: • Atomic transactions • Compensatable transactions • Reporting transactions • Co-transactions

26. Kangaroo Transaction Model(Dunham et al) • DAA (Data Access Agent) acts as transaction manager at base station • For each transaction request DAA generates… • For each hop a new Joey is created. • When a Joey fails, all previous Joeys and KT will abort. • A Kangaroo Transaction (KT) at MH • A set of Local Transactions (LTs) & Global Transactions (GTs) at local base station called as Jeo Transaction (JT).

27. Fig 5: Kangaroo Transaction Model

28. The Clustering Model(Pitoura et al) • Based on the extended open-nested transaction model. • Database is divided into clusters defined statically or dynamically. • Based on consistency requirement, Transactions and Operations are divided into two sets- weak and strict transactions. • A weak operation can access only the local copies of a data item (i.e. within the cluster). Strict operations are allowed to access all the clusters. • Weak operations are committed for two times, first in local cluster and second across clusters.

29. Isolation-Only Transactions (Satyanarayan et al) • provides an application transparent file system (by hoarding highly prioritized files) • concurrency control for mobile clients. • proxy maintains log information during disconnection and updates the information on reconnection. • detects read/write conflicts automatically during disconnections. • does not guarantee failure atomicity.

30. Two-tier Model(Gary et al) • Master data copy exists in the fixed network. • Transactions at fixed stations are called base transactions. • Transactions carried out at the disconnected mobile hosts are called tentative transactions. • At the reprocessing stage, application semantics and serialization applied to increase concurrency of the transactions. • Model uses a history-based approach for reprocessing.

31. Team Transaction model(Gore and Ghosh) • Designed to deal with mobile transactions in Ad hoc networks • - Team Transaction consists of three entities: • 1) Coordinator 2) Players 3) Data Access Agent (DAA). These entities form a cluster. • Coordinator is captain of the team and responsible for coordinating the operations of transactions. • Players carry the operations of sub-transactions assigned by coordinator. • - DAA provides database access, maintains log information for recovery, and keeps track of the coordinator and selects new coordinator incase of crash.

32. Fig 6: Team Transaction Model

33. Multi-database Transactions(Yeo and Zaslavsky) • Main goals are transparency, concurrency, availability and recovery. • Multi-database system is an integrated distributed system of • local and global transaction management components global communication manager • global recovery manager • interface managers

34. Fig 7: Architecture of MDSTPM

35. Toggle Transactions(Dirckze and Gruenwald) • similar to Multi-database scheme. • a Mobile Multidatabase System (MMDBS) is defined as a collection of fixed and mobile databases. • MMDBMS is a DBMS software, resides on fixed network and controls respective database systems. • Global transactions access MMDBMS. • Local transactions use local database. • Global transactions: • Site-transaction is a subset of global transactions which access the same site. • migrating transactions support the mobility of the users.

36. PRO-MOTION(Crysanthis) • Based on client-server architecture. • Supports disconnected transaction processing. • Considers the entire mobile sub-system as a large, long-lived transaction • Each sub-transaction is again the root of another nested split transaction. • A compact is an agreement between server and host. • Mobile hosts execute a piece of code called compact agent to handle requests. • An intermediate mobile manager (MM) on the mobile service station handles compact agent and writes log information. • Compact manager (CM) executes on the server provides nested-split transaction processing capability.

37. Fig 8: PRO-MOTION System Architecture

38. Table 2: Comparison of Transaction Models

39. 5. Query Processing • Location Dependent Query Processing • QBI (Query by Icons) • Using Summary Databases

40. Location Dependent Query Processing (LDPQ) • - Queries contain location related and non-location related attributes. • Current position of the query issuer is implicitly involved in the query. • ex: “Find hospitals within 10 miles” • This implied location related information will be added to the query. • Location service binds the current location to the query and this binding is known as location binding.

41. Query By Icons(Antonio Massari) • QBI include: • An iconic visual language interface that allows users to compose queries by using a pointing device like a pen to manipulate icons. • A semantic data model that captures most of the aspects of database structures. • Metaquery tools that assist on the formulation of queries during periods of disconnection.

42. QBI Architecture • The architecture consists of four modules: • Presentation Manager: responsible for all user interactions • Query Manager: supports the specification of queries. • GA Evaluator: computes the generalized attributes • Database Access Manager:is responsible for any remote access to the data on a fixed host, data updates and metadata management.

43. Fig 9: QBI Architecture

44. Query Processing using Summary Databases(Madria et al) • A condensed form of the main database, which is termed as “summary database” is used in replication. • Summary databases are small in size and can answer the queries approximately during disconnection or weak connection. • There are three types of connections between host and MSS: connected, partially connected, disconnected. • The query processor selects main database or summary databases depending on the connection status. • Query processor rephrases the queries to access summary database.

45. Query Processing using Summary Databases(contd..) • Summary databases use concept hierarchies. • Concept hierarchy is a result of mapping from one level to another level of data abstractions. • A concept hierarchy has a tree or lattice structure of concepts at different levels of abstraction. • Summarization of the data can take place in two ways: • Horizontal summarization (involves attributes of a relation) • Vertical summarization (involves tuples of a relation)

46. Fig 10: Mobile Database Environment with Summary Databases

47. 6. Recovery • Recovery Protocols • Recovery Guarantees

48. Recovery Protocols( M. M.Gore and R. K. Ghosh) 1.Timeout protocol: executed by MSS. MSS maintains a timer to measure the inactivity period of mobile host and initiates rollback for the transaction on timeout. 2.Disconnect protocol: executed by mobile host due to resource problems (like battery discharge, weak signal etc.). 3. Hand-off protocol: executed by mobile host, when it switches from one MSS to another MSS. Mobile host sends it’s new MSS address to the old MSS and conveys old MSS information to the new MSS while switching from cell to cell. 4. Migration protocol: In this protocol migration information and new settings of mobile host are communicated to the old MSS by the new MSS, before timeout or disconnect protocol execution at old MSS

49. Fig 11: Mobile Transaction Recovery Protocols

50. Recovery Guarantees(Martin and Krithi Ramamritham) • Recovery guarantee is a recovery assurance of one subsystem (eg.MSS) to another subsystem (eg.MH) in case of failures. • Protocol: • ifp succeeds • then q will also succeed, if invoked • The guarantee of assurance by a subsystem is up to its capabilities. • The guarantee can be given by any subsystem other than the system where operation p is executed. • Recovery protocols are prescriptions based on the recovery guarantees of the system. These protocols satisfy precedence constraints.